I don't lead with a ladder discussion but if a prospect asks I have this home made flyer to hand.
Dear Mr. Newcusty:-
MalcGold window cleaning welcomes you as a new customer and we hope you don't mind a word about safety:-
If your window cleaner falls from his/her ladder on your property and injures himself or damages your (eg) vehicle is it?:-
A) His problem - surely he carried out correct risk assessment procedures beforehand?
B) Your problem - you should know whether he can use a ladder on your property for cleaning windows or not.
C) His insurer's problem (if he has any) - but will they pay out?
D) Your insurer's problem - but will they pay out?
E) Who knows until it goes to court? (With all the attendant hassle beforehand)
In all honesty as your window cleaner I would say "E" above - so I personally follow HSE guidelines and choose what I believe to be the safest method to clean your windows. I believe the safest method for your property is a Waterfed Pole System. I know my insurer is aware I use the system and the first question in the HSE guidelines for window cleaning about ladder access is "Can the work be done from the ground (eg WFP)"
If a ladder-using window cleaner should approach you and say that his method is perfectly ok to use then perhaps you could put the above questions to him and gauge his response?
I used this on one "blow-hard" fella out canvassing three months ago and left it with him - three days later he phoned and asked me to do his windows. He seems happy so far ...
It's the way you tell 'em!